Two live attenuated parainfluenza virus type 3 (PIV3) candidate vaccines have completed Phase I trials in human infants and children. A bovine PIV3 that is antigenically related to the human PIV3 is in the final stages of licensure to a biotechnology company that will pursue its further development. The second candidate, the cold-passaged (cp45) mutant of human PIV3, is being studied further under a CRADA between NIAID/LID and a pharmaceutical manufacturer. This candidate vaccine virus replicates to high titer in a licensed cell substrate and clinical lots of vaccine virus that are attenuated and stable phenotypically in monkeys will be evaluated this year in humans. A highly attenuated vaccinia virus vector (MVA), that should be completely safe for immunocompromised humans, was used to express the viral surface HN and F glycoproteins that are the major protective antigens of PIV3. Immunization of rhesus monkeys with the MVA-PIV3 recombinant viruses induced complete protection against infection by a wild type (wt) PIV3 challenge.